Treatment process

ABSTRACT

Given a group of radioactive concentrates including a concentrate from a resin-bead ion exchange filter, a concentrate from an evaporation concentrator, and a concentrate from another concentrator yielding a concentrate having a salt content lower than that of the concentrate from the evaporation concentrator and particles smaller than the particle size of the resin beads; a process including mixing the concentrate from the resin-bead ion exchange filter with the concentrate from the other concentrator, passing the resulting mixture through a filtercake-producing filter for dewatering and drying, and skirting the concentrates from the evaporation concentrator around the filtercake-producing filter and directly into transport and storage vessels for their dewatering in such vessels.

Unite States Patent Queiser et a1.

[ NOV. 20, 1973 TREATMENT PROCESS Appl. No.: 119,339

[73] Assignee:

3,360,869 1/1968 Muller 210/68 X Primary Examiner-John Adee Attrney-Spencer & Kaye [5 7 ABSTRACT Given a group of radioactive concentrates including a concentrate from a resin-bead ion exchange filter, a concentrate from an evaporation concentrator, and a concentrate from another concentrator yielding a concentrate having a salt content lower than that of the Foreign Application Priority Data concentrate from the evaporation concentrator and Jul 20 970 German P 20 925 5 particles smaller than the particle size of the resin y y beads; a process including mixing the concentrate from the resin-bead ion exchange filter with the con- 'C 210/68 8 centrate from the other concentrator, passing the re- I Suiting mixture through a filter cake producing filter [58] Field of Search 210/68, 70, 71, 73 for dewatering and y g, and skirting the concen trates from the evaporation concentrator around the [56] References cued filter-cake-producing filter and directly into transport UNITED STATES PATENTS and storage vessels for their dewatering in such ves- 2,624,955 1 1955 Robison 210/68 x se1s 2,081,398 5/1937 Giles 210/68 3,482,693 12/1969 Muller 210/71 X 7 Claims, 1 Drawing Figure NUCLEAR POWER PLANT J50 2- j 3 Z Z, 5 6 s7,

1 1 s *{49 I 50 s/ 52 L 1 Q TREATMENT PROCESS BACKGROUND OF THE INVENTION The present invention relates to a method for decreasing the liquid content of radioactive concentrates.

As described in the article Abfallbehandlung (in translation Waste Treatment), which appeared in the November, 1965, issue of Atomwirtschaft, pages 624-626, processing of radioactive liquid wastes, for instance those occurring in nuclear power plants, is usually done in three parts:

1. Filtration through mechanical filters with the filtrate being then passed through ion exchangers;

2. Concentration in evaporators;

3. Filtration only through mechanical filters.

The first-listed part is used for the waste waters from the nuclear cooling system and from the condensation system (these waters make up 60 percent to 70 percent of the total waste-water load).

The second-listed part is used for sump waters, laboratory waste waters, and decontamination waters from the entire control region (about 20 percent to 30 percent of the total waste-water load).

The third-listed part is used for cleaning wash waters from washing machines, showers, and hand-washing basins, as well as inactive laboratory waters from the control region (about 5 percent to percent of the total waste water-load).

From these water-processing steps and other cleaning operations large amounts of radioactive concentrates arise. Efficient service organizations for collecting and treating these concentrates do not exist. A storing of these concentrates in liquid form is presently not possible. The processes used in Europe for handling these concentrates involve the use of additive materials such as bitumen, concrete, oil shale ash, and bone size. These add to the total volume of the final material to be disposed of. They have often required too great of a capital investment.

The storing of these concentrates for the purpose of allowing radioactive decay to run its course requires considerable capital expense, especially where waste quantities are large, such as in the case of large power plants. It therefore becomes worthwhile to dewater and solidify such concentrates.

In efforts thus far made toward dewatering and solidification, a number of problems have arisen which have to this time prevented widespread acceptance. Among the problems are the following:

1. The concentrates occurring are very variable in their compositions. A primary problem here is that waste waters from resin-bead ion exchange filters can not be dewatered with a usual filter-cake-producing filter, because the resin beads as a result of their shape do not remain lying on the filter cloth or septum especially once their moisture content has sunk below a certain level. Because of this problem, filter-cake-producing filters have been automatically dropped from consideration whenever a concentrate containing resin beads must be dewatered.

2. The concentrates occurring have very different activity loads.

3. The dewatered and solidified material must satisfy current governmental requirements for the storage of radioactive wastes.

4. The packaging must meet the requirements for the transport of dangerous materials as set for international railroad freight traffic.

SUMMARY OF THE INVENTION An object of the present invention, therefore, is to provide a simple process for the treatment of radioactive concentrates arising in the above-listed parts.

Another object is to produce a minimum waste concentrate volume, which lacks additive materials.

Yet another object is to produce with especially small capital and operational costs a much drier radioactive waste residue than heretofore.

Yet another object is to produce a dry residue which can be cheaply transported and stored in containers.

These as well as other objects which will become apparent in the discussion that follows are achieved, according to the present invention, in the following manner. Given separate concentrates from an evaporation concentrator, from a resin-bead ion exchange filter system, and from at least one other concentrating stage, for instance from mechanical filters, settling basins, and/or powdered-resin ion exchange filters, that from the one other stage being characterized by a smaller particle size than that from the resin-bead ion exchange filter and by a lower salt content than that from the evaporation concentrator, the concentrate from the resin-bead ion exchange fiber is mixed with the concentrate from the other stage and the resultant mixture is then fed to a filter-cake-producing filter for dewatering and drying, while the concentrate from the evaporation concentrator is skirted around the filter-cakeproducing filter, without its passing through the filtercake-producing filter or in any way coming into contact with the filter cake of the filter-cake-producing filter, directly into transport and storage containers where it is brought to the desired dryness for storage. In the mixture, the ratio of the one other concentrate to the resinbead concentrate must be at least a certain minimum value such that the resin beads do not fall out of the drying filter cake.

It has been discovered that this mixing of the concentrate from the resin-bead ion exchange filter with the concentrate from the one other concentrator has the particularly advantageous result that when the mixture is fed to the filter-cake-producing filter, the resin beads become bedded into the resulting filter cake and their dewatering and drying therefore becomes possible without their falling from the filter cloth or septum once their moisture content has sunk below a certain level. Consequently, only the relatively small volume of concentrate from the evaporation concentrator needs to be dried using the more costly, heat-energy consuming method of evaporating the remaining liquid from the concentrate.

The nuclear power plants Wurgassen, Brunsbuttelk- 00g and Phillipsburg are being prepared to use the present invention.

The feeding of the concentrate from the evaporation concentrator to the filter-cake-forming filter which processes the mixture of resin-bead concentrate and one other concentrate is not practicable, because the high salt content in the concentrate from the evaporation concentrator would cause the filtrate to achieve such a high salt concentration that it could not be recirculated into the works without the expensive further treatment of reducing thishigh salt content.

BRIEF DESCRIPTICN OF THE DRAWING TRAIION (ALKALINE plI OF ABOUT 10) 1. Composition of tho solids (al. 20" Amount of solids- 8.3 /lllo ml.

ilifiin IlL-C6lVlPOSITION OF EVARORATTQN'CONCEN DESCRIPTION or THE PREFERRED Particle 73%;; EMBODIMENTS Name Chemical formula size percent l 1ft N so, 11 Ab r20 11 The schematic diagram of the FIGURE illustrates a jiit iciiii n s uiiaie nn l iiu ia i i bit 20';

eav meta oxi es.-. .g. ez 3 pri- F treatment plant for practicing the present invention on Y mmly) plus Ono the waste concentrates from a large light-water nuclear C I h h t cgrzgiglanfi 1 t 0 power plant 80 using a boiling water reactor manufacglgfifgffggf- 2 6 6 52 351155;:1: i tured by AEG-Telefunken. Container 1 carries concengl g ififg g granulartrate entering through pipeline 45 and resulting from almnim m sili cates condensate cleaning. Container 2 collects concentrate (more 8 us from pipeline 46 resulting from mechanically filtering W 7 "4 W the wash waters coming from the entire control region. compqslflvn 0f th diss lved material Evaporation residue=8.27 g./100 ml. Container 3 has a resin-bead concentrate from mixed bed ion exchange filters entering through pipeline 47. Chemical 33:8 Containers 4 and 5 contain concentrate resulting from Name Symbol percent cleaning the reactor water. Container 6 collects the a concentrate from an evaporation concentrator, as congs 3 8, trasted with containers 1 to 5 whose concentrates result g3 55 from filtering operations. Up to Exemplary data concerning the concentrate compo- I g8 g9 sitions of the various containers is given in Tables I to ill. Approximate values, =106 meters.

TABLE L ooNEENT RATE EFMEBH6N Relative slurry Solids in Period*, Concentrate volume, mfl slurry, kg. days Solids type 1. Filter concentrates:

(a) Container 1:

Normal operation 74 3,000 100 Powdered resin with corrosion products. Cooling water break-in. 74 3, 000 10 Do. (b) Containers 4 and 5 10 20 5 Do. (c) Container 2 4. 5 144 1 See Table II. ((1) Container3 8 3,000 00 D0. 2. Evaporation concentrate: Container 6 2. 6 360-620 10 See Table III.

*Period is defined as the normal supply period of the concentrates. Evaporation residue.

-""EX1JE ir riL' r a ir-t c o onN'I EATE EBME$ITI0NS (NEUTRAL on sLIonTLY ALKITNEY Relative amount in any given con- Chemical identity Particle Distribution in centrate m N anie and form; wt. percent size wt. percent wt. percent Kieselguhr filter aid, Celito 545 SlOz, 89.6%, A120 4.0%, NazO and K10,

3.3%, granular.

Activated carbon filter aid, Synofils Solkafiocken BW 100 Comminuted charcoal, granular Fine cotton hairs.

Hgaxpggs metal hydroxides or hydrated mainly iron Up to 50%.

)3 Dispersed hydroxides... 4% mainly chromium and nickeL. 1.2 mm 1 Mixed bed filter resins Carbonyl synthetic resin ion exchanger 0.8-l.2 1o

1 head shaped. 0.34-0 Up to Powderedresi Comminuted mixed bed filter materiai OIOSiiiin p to Colcium-sihcon and aluminum oxides CaO4SiO2+Al O granular (concrete dust). 20-100, P

or calcium and aluminum silicates. Dust and small amounts of oil (where (Soot) p to p=10 meters). Oil Up t0 Floccnleni.

The concentrates in containers 1, 2, 4 and 5 have a salt content lower than that of the concentrate in container 6 and particles of a size smaller than the particle size of the resin-beads in container 3.

The concentrates of containers 1 through 5 can be fed to the intermediate storage container 9 through pipelines 60 to 67 by concentrate pumps 7 and 8. Pipelines 60 to 64 include individually controllable valves 72 to 76 so that any desired mixture can be obtained in container 9.

Stirrer 10 serves to mix the concentrates fed into container 9. From container 9, the resulting mixture is fed through pipeline 69 by pump 68 to a filter-cakeproducing filter 11. This filter 11 is made of a number of plate-shaped elements 13 carried by a vertical, hollow shaft 12. Filter cake forms on the upper sides of the plates. The filtrate is drawn off through the hollow shaft 12 and pipelines 34, 38 and 39 and drained into storage vessels or passed to further water treatment and then recycled.

An example of filter 11 is a steam heated filter obtainable under the designation Funda- Rueckstandsfilter R10 from Chemap AG, Maennedorf/Zuerich, Alte Landstr. 414. Another example of filter 11 is that described on pages 19-72 and 19-73 of Chemical Engineers Handbook, by John H. Perry, McGraw-Hill Book Co., New York (4th Ed., 1963) under the heading The Rodney Hunt Pressure Filter.

In order to prevent radioactive solids from getting into the filtrate, filter 1 1 is first provided with a precoat of fibrous material, such as cellulose fiber, before actual filtration begins. To this end, there is provided a precoat tank 14 connected in an auxiliary circuit. The fibrous material is first thoroughly mixed with water in the precoat tank; then this fiber-laden water is pumped by pump 37 into the filter while a suction is being applied to shaft 12, whereby the precoat is formed on the filter cloths or Septa of the elements 13. An example of a suitable fibrous material is clean, fibrous cellulose material designated as Type BW 100 (cotton fibers of 1 millimeter length). During drying, this cotton fiber precoat gives an effect equal to a paper filter and acts to filter out aerosols.

The cotton fibers are added to water in tank 14 until they amount to 3 to 4 weight-percent of the weight of the water. A homogenizing period during which the fiber-water mixture is circulated through the filter and the precoat tank via pipelines 34, 35, and 36 by pump 37 assures a uniform precoat layer thickness of about 0.8 millimeters.

The solids in container 9 can only contain up to 25 weight-percent resin beads from container 3. Exceeding of this limit leads to an unstable filter cake from which the resin beads can fall during dewatering and drying. Under this limit, the resin beads become securely embedded with the other waste solids in the filter cake and are held there throughout dewatering and drying.

When an economical filter cake load has been built up on elements 13, any remaining, unfiltered slurry remaining in filter 11 is circuited back to container 9 through pipeline 44 and dewatering and drying is then carried out in a two-phase process. First, the excess water is blown out of the filter cake with a flow of 20 C air equal to a flow rate of 200 standard cubic meters per hour per square meter of filter area, where the conditions for the standard cubic meter are 0 C and 760 mm Hg. When the removal of liquid water has substantially ceased, the filter cake is dried with a flow of 120 C air equal to a flow rate of standard cubic meters per square meter of filter area per hour.

Air is brought into filter 11 by blower 22 through conduits 41 and 42 and 43. Electrical air heater 23 raises the temperature of the air for the second phase of the dewatering and drying process. Air is exhausted through lines 34 and 38 and conduit 40. Air cooler 24 removes any condensable components from the air before it reaches exhaust chimney 33.

The dried filter cake is removed from elements 13 by rotating shaft 12 by means of motor M at 300 rpm. The filter cake is flung centrifugally from the elements 13. Below filter 11 there is a residue bin 15 through which the dried filter cake from the filter 11 is conducted into containers 16. The bulk density of the dried powered filter cake in the container 16 lies between 0.65 and 0.8 t/m, where t=1,000kg and m meters.

The air used during the two-phase dewatering and drying may be passed through an air filter to remove any suspended solids before exhausting it to the atmosphere.

The relatively small volumes of concentrate coming through pipeline 58 into container 6 from the evaporation concentrator are conducted directly from container 6 through pipeline 59 into transport and storage containers 17 which have been previously attached to drying hood 18. The concentrate flow from container 6 is stopped when level indicator 19 indicates that a predetermined concentrate level has been achieved.

Hood 8 contains infrared radiators which heat the concentrate in a container 17 from above. Air flow within the hood is controlled so that it passes over the liquid surface of the concentrate and withdraws vapor as it is produced by the radiators. A thermally caused circulating of the liquid concentrate in a container 17 prevents premature crusting on the sides of the container. Maintenance of the air flow within the hood and over the surface of the concentrate makes the hood and container interior have a negative pressure, so that no vapors can escape through any leaks at the connection between hood and container.

When no liquid level remains, a post drying period is initiated to bring the moisture down to less than 30 weight-percent of the total weight of drey residue. This mositure content is generally sufficient to prevent indications of fermentation and decay and to reduce the possibility of corrosion sufiiciently that the filled containers can be stored for years without developing leakages. The bulk density of the powdered residue left in container 17, lies between 0.8 and 1.5 t/m where t 1,000 kilograms and m meters.

This procedure for handling evaporation concentrates is presently being used in an installation at the AEG Nuclear Energy Experimentation Center Grosswelzheim. The installation can process 10 to 20 liters of evaporation concentrate per hour.

Air flow through hood 18 comes in from conduit 30 and has been heated by heater 31. Exhaust air laden with vapor leaves through conduit 32. The exhaust air is passed through a combined cyclone/sand filter unit 20 to remove any solid or liquid particles and is then forwarded by airtight blower 21. The exhaust air then passes through dry air cooler 24, where any condensable components are removed, and thence to exhaust chimney 33. Condensate and rinse water from the cyclone/sand filter are returned to container 6.

A suitable container 16 and 17, together with lid, is set forth on page 94 of the journal Atompraxis ,Vol. 16, No. 2, 1970.

Since the concentrate resulting from cleaning the re actor water often exhibits higher radioactivities, special containers are provided for the collection. At least two containers 4 and 5 are always provided, so that alternatively one and then the other can be filled, through pipelines 57 and 55 and valve 77, and through pipelines 57 and 56 and valve 78. This allows an optimum storage time to be selected for allowing radioactive decay to proceed partially before the concentrates are forwarded to container 9 from the container 4 or 5 which at the moment is not being filled.

The containers 1-5 are sedimentation tanks, so that it is possible to allow a more complete sedimentation of solids within them and to forward the cleared waters directly to further water processing through pipelines 48 to 54 using pumps 70 and 71, without passing them through filter 1 1. This operates to reduce the work load of filter 11. The water forwarded through pipeline 53 by pump 70 goes to the sump system of the plant, while the water forwarded through pipeline 54 by pump 71 goes to the mixed bed ion exchange filters, Filtercake-producing filters" is used herein to distinguish from those filters which operate exclusively by ionexchange capture of the substance to be filtered out.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations and the same are in tended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. A method for removing liquid from radioactive concentrates from a nuclear plant, comprising the steps of: mixing a resin-bead, radioactive concentrate of said plant from a resinbead ion exchange filter with a radioactive concentrate of said plant having particles of a size smaller than the particle size of the resin-beads of said ion exchange filter; dewatering and drying by passing the resulting mixture through a filter-cakeproducing filter; the step of mixing producing a mixture wherein the ratio of the smaller-particle-size concentrate to the resin-bead concentrate is sufficiently large than the resin beads remain stably emplaced in the resulting cake on the filter even after the cake is dry; skirting a radioactive evaporation-concentratorproduced concentrate of said plant of salt content higher than that of the smaller-particle-size concentrate around the filter-cake-producing filter and directly into transport and storage vessels; and dewatering and drying in the transport and storage vessels the concentrate from the evaporation concentrator down to a water content required for storage.

2. A method as claimed in claim 1, the filtercakeproducing filter comprising a plurality of plate-shaped elements carried by a vertical hollow shaft means for removing filtrate, filter cake forming on the upper sides of the plate-shaped elements during filtering, further comprising the step of coating on the elements a precoat of fibrous material for filtering out radioactive solids.

3. A method as claimed in claim 2, the fibrous material being cellulose fiber.

4. A method as claimed in claim 2, the step of coating being additionally for filtering out aerosols during drymg.

5. A method as claimed in claim 1, further comprising, before the step of dewatering and drying by pass ing, the step of settling solids from the concentrates.

6. A method as claimed in claim 1, the step of mixing being performed in an intermediate storage container having a means for mixing concentrates fed into it.

7 A method as claimed in claim 1, the smallerparticle-size concentrate having a relatively high radioactivity, further comprising the steps of filling this smaller-particle-size concentrate sequentially into a plurality of containers and performing the step of mixing with the concentrate from the earliest-filled of said plurality. 

2. A method as claimed in claim 1, the filter-cake-producing filter comprising a plurality of plate-shaped elements carried by a vertical hollow shaft means for removing filtrate, filter cake forming on the upper sides of the plate-shaped elements during filtering, further comprising the step of coating on the elements a precoat of fibrous material for filtering out radioactive solids.
 3. A method as claimed in claim 2, the fibrous material being cellulose fiber.
 4. A method as claimed in claim 2, the step of coating being additionally for filtering out aerosols during drying.
 5. A method as claimed in claim 1, further comprising, before the step of dewatering and drying by passing, the step of settling soLids from the concentrates.
 6. A method as claimed in claim 1, the step of mixing being performed in an intermediate storage container having a means for mixing concentrates fed into it.
 7. A method as claimed in claim 1, the smaller-particle-size concentrate having a relatively high radioactivity, further comprising the steps of filling this smaller-particle-size concentrate sequentially into a plurality of containers and performing the step of mixing with the concentrate from the earliest-filled of said plurality. 